A series of huge explosions tore through the regime-held heart of Syria's
biggest city levelling major Aleppo buildings and killing scores of people,
many of them soldiers.

At least two and possibly three explosions struck the main Saadallah Jabri square, the seat of a number of important government buildings, along with two government-owned hotels, a military Officers' Club, and a telecoms office.

Television footage and photographs from the scene, which is near the front line between rebels and regime forces in the city, showed the Officers' Club and telecoms building reduced to a pile of rubble.

The once impressive facade of the Riga Palace Hotel was left a ragged patchwork of concrete. A further bomb just off the square, near Bab Jenine, wreaked similar damage on the chamber of commerce.

Syria's state news agency put the death toll at 31 people, whilst the Syrian Observatory for Human Rights said 48 people were killed.

Residents told The Daily Telegraph that most of the victims were members of the security forces lodging in the buildings during the fighting which has consumed the city since mid-July.

"This area was where the regime housed many of its officers, and the hotels were full of its soldiers," said a resident and opposition activist who called himself Abo Hamdo and who had just returned from the scene. "Very few people that were not from the security forces had been allowed close to the Officers' Club in the past few days.

"The bombs struck at 8am, so very few shop owners or other civilians were in the area."

State media said the explosions were caused by suicide car bombers, and the footage showed a huge crater in the road nearby though no vehicle wreckage. The rest of the square, which connects the historic, UNESCO-listed Old City to the south-east with the municipal park and prosperous, regime-held new city to the north and west, was reduced to dust.

"The soldiers have cleared away the dead and wounded. There are just shoes from the victims and some blood left," said Abo Hamdo, who said his office was also destroyed in the blast.

The scale of the damage suggested far bigger explosive charges than those seen in previous car bombings, and there were immediate, competing conspiracy theories circulated as to whether the government version of events was true.

According to one account, the target may have been President Assad himself, who was rumoured to be on a visit to Aleppo, though there was no corroboration of this and it would be highly dangerous for him at present.

Some residents reported seeing jets in the area, though there was no explanation for what the government could hope to gain by staging an attack behind its own lines. More credibly, there were suggestions that the attacks could have been an "inside job" owing to the difficulty the Free Syrian Army would have had in getting cars laden with explosives through the many government checkpoints on roads leading to the square.

State television showed the supposed bodies of the suicide bombers, one still clutching a detonator, wearing army uniforms "as a disguise", leading some to suggest they were defectors.

Leaders of the Free Syrian Army outside the country seemed to be caught by surprise by the attack.

"From the FSA no one is responsible," said Louay Mokdad, a spokesman for the Military Council, the formal element of the FSA leadership.

"We are fighting in Aleppo and there is a battle in Aleppo. We don't need some car bombs."

On the other hand, an online video purporting to be from Jabhat al-Nusra, a jihadist group accused of ties to Al-Qaeda, later claimed responsibility.

The blasts risk further alienating Aleppo residents, many of whom conspicuously refused to join protests against the Assad regime. The nearby bazaar, mostly now in rebel hands, was largely destroyed by fire over the weekend.

The war in the north of Syria is gradually slipping away from Mr Assad, but with growing "collateral damage".

Rebels who seized the northern border post with Turkey at Tal al-Abyad last month are now reported to be moving on the government held town of al-Raqqah that has become home to up to hundreds of thousands displaced.

Regime mortar fire aimed at rebel positions at Tal al-Abyad fell on the wrong side of the border, killing five people including a woman and her three children in the Turkish town of Akcakale, prompting the Turkish government to lodge a protest with the United Nations.